This invention relates generally to signal processing and more particularly to a method of identifying which of a large number of received pulses was emitted by a particular signal source.
In certain signal environments, one receiver may be simultaneously exposed to pulsed signals transmitted by a plurality of signal sources, or "emitters". To obtain the maximum amount of useful information, the receiver must group the received pulses according to their source. This process, sometimes called "pulse sorting", allows the signals from each of the emitters to be processed separately. Such a technique is beneficial because it allows a reduction in the complexity of the processing performed by the receiver. Pulses associated with emitters which provide little information can be ignored. Spurious pulses not associated with any emitter need not be processed.
One known way to accomplish pulse sorting is called "histogramming". This technique takes advantage of the fact that most emitters which transmit pulsed signals transmit pulses at regular intervals. To perform histogramming, the receiver keeps track of the time of arrival of each pulse. For each received pulse, the difference between the time of arrival of that pulse and all preceeding pulses is added to the histogram. As a simple example, if a pulse is received from a particular emitter every 6 seconds, after one minute, the histogram will contain, among other entries, 10 entries associated with the time six seconds. The 10 entries likely represent a local maximum or peak in the histogram. Thus, to identify various emitters, a receiver searches for peaks in the histogram.
One drawback of this approach is that to produce accurate results, the histogram must be constructed from a sufficient number of pulses. Since it takes time to collect the required number of pulses, it takes a correspondingly long time to associate pulses with an emitter using histogramming. Further, some emitters produce pulses at rates up to a thousand times faster than others. Since, in the histogram, the peaks associated with pulses at the higher rate will be much larger than peaks associated with pulses produced at the lower rate, substantial processing is required to identify pulses at the lower rate. Searching through all the entries in the histogram can also require more processing than is desirable in some instances.